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There's a standard ogee bit (I think it's called a reverse ogee) that will do the typical profile in two passes. You set the bit for the full ogee cut to do the underside; then raise the bit so that you just do a round-over on top.
I use 1 1/2" to 1 3/4" reveal on each side because it allows me to cut my returns in my miter box cleanly. I let the stool stand proud of the wall by whatever the stock comes in, i.e., if the stool material is 5 1/4" and the window opening is 4 1/2" deep, I end up with about a 3/4" jut.
I've done deeper stools for potted plants and such in areas that will not be obtrusive.
Those wider stools can look really nice. I made an elaborate window for my brother and his wife using 5/4 by 12" clear pine for the stool. I was hesitant to do it but it came out looking nice. It is used as a breakfast table, I made corbels to support the stool and used tile/wood trim combination for the "apron" that runs between the corbels. The rest of the window is dressed up with sides to mimic columns and the top is built out with crown.